Production of polymers that are derived from renewable resources is expected to grow to 3.45 million tons by the year 2020 which represents a current annual growth rate of approximately 37% (Plastics Engineering, February 2010, p 16-19). The drivers for growth of biobased plastics include the contribution to global warming from production of petroleum-based plastics, the need to reduce our dependence on limited supplies of petroleum oil, the fluctuating petroleum oil prices as well as environmental disposal problems of common petroleum-based plastics. While the objective for the manufacture of biobased plastics is to maximize the total “renewable” carbon content of polymer products as much as possible, some existing large volume biobased plastics have unique material properties which can be utilized as value-added modifiers for existing petroleum-based plastics and composites.
Examples of biobased polymers include polyethylene (PE) produced from sugarcane ethanol (Braskem's Green Polyethylene), polylactic acid (PLA) made from corn sugar (Nature Works Ingeo™ PLA) and polyhydroxyalkanoates (PHA's) produced by the fermentation of glucose (U.S. Pat. Nos. 6,593,116 and 6,913,911, US Patent Pub. No. 2010/0168481). Reportedly, the most commercially important bioplastics by the year 2020 will include starch-based polymers, PLA, polyethylene, polyethylene terephthalate (PET), PHA and epoxy resins (Shen et al., (2010), Biofuels, Bioproducts and Biorefining, vol. 4, Iss. 1, p 25-49).
Polyhydroxyalkanoates (PHAs) are perhaps uniquely positioned to be value added modifiers for plastics as they can be produced with a range of material properties from hard and brittle to soft and flexible. PHAs are naturally produced by numerous microorganisms in diverse environments. Through genetic-modification of these microbes, hundreds of different types of biobased PHA homopolymer and copolymer materials have been developed (Lee (1996), Biotechnology & Bioengineering 49:1-14; Braunegg et al. (1998), J. Biotechnology 65:127-161; Madison, L. L. and Huisman, G. W. (1999), Metabolic Engineering of Poly-3-Hydroxyalkanoates; From DNA to Plastic, in: Microbiol. Mol. Biol. Rev. 63:21-53). However based on these unique properties and the demonstration of their performance benefits, it is also possible to chemically synthesize other PHA polymers from renewable or petroleum resources to achieve similar performance advantages.